Fuel cells electrochemically convert fuels and oxidants to electricity and heat and can be categorized according to the type of electrolyte (e.g., solid oxide, molten carbonate, alkaline, phosphoric acid or solid polymer) used to accommodate ion transfer during operation. Moreover, fuel cell assemblies can be employed in many (e.g., automotive to aerospace to industrial to residential) environments, for multiple applications.
A Proton Exchange Membrane (hereinafter “PEM”) fuel cell converts the chemical energy of fuels such as hydrogen and oxidants such as air directly into electrical energy. The PEM is a sold polymer electrolyte that permits the passage of protons (i.e., H+ ions) from the “anode” side of the fuel cell to the “cathode” side of the fuel cell while preventing passage therethrough of reactant fluids (e.g., hydrogen and air gases). The Membrane Electrode Assembly (hereinafter “MEA”) is placed between two electrically conductive plates, each of which has a flow passage to direct the fuel to the anode side and oxidant to the cathode side of the PEM.
Two or more fuel cells can be connected together to increase the overall power output of the assembly. Generally, the cells are connected in series, wherein one side of a plate serves as an anode plate for one cell and the other side of the plate is the cathode plate for the adjacent cell. Such a series of connected multiple fuel cells is referred to as a fuel cell stack. The stack typically includes means for directing the fuel and the oxidant to the anode and cathode flow field channels, respectively. The stack usually includes a mechanism for directing a coolant fluid to interior channels within the stack to absorb heat generated by the exothermic reaction of hydrogen and oxygen within the fuel cells. The stack generally includes mechanisms for exhausting the excess fuel and oxidant gases, as well as product water.
The stack also includes an endplate, insulators, membrane electrode assemblies (MEA), gaskets, separator plates, electrical connectors and collector plates, among other components, that are integrated together to form the working stack designed to produce electricity. The different plates may be abutted against each other and connected to each other to facilitate the performance of particular functions.
The MEA is formed of a membrane, catalyst layers and gas diffusion layers. The manufacture of an MEA can result in a relatively hard perimeter being formed on a gas diffusion layer (GDL) of the MEA that does not easily compress when it contacts a flat area of a plate housing fluid flow channels adjacent to the flow field channels. It is desirable for a fuel cell stack to have enough compression of the GDLs to ensure good contact and low electrical resistance between GDL and plate, and also between GDL and membrane. Because of this hard perimeter in some MEA constructions, the force required to compress the stack to a desirable amount of GDL compression can become excessive. With excessive force required, additional structure must be added to endplates, compression members (springs), and tensioning members of the stack.
Thus, there is a need for improved fuel cell systems and improved methods of manufacturing fuel cells that minimize the force required to efficiently assemble a fuel cell stack.